Soil Cation Research Articles

Revitalizing the Biochemical Soil Properties of Degraded Coastal Soil Using Prosopis juliflora Biochar.

Biochar is an effective soil amendment with capabilities of boosting carbon sequestration and enhancing soil fertility, thus enhancing plant growth and productivity. While numerous studies have documented the positive effects of biochar on improving soil properties, a number of studies have reported conflicting results. Therefore, the current study was conducted to evaluate the impact of Prosopis juliflora biochar (0, 2.5, 5.0, and 7.5 t ha-1) on soil biochemical properties in Coastal Kenya to ascertain biochar's potential for soil fertility improvement. A randomized complete block design was used for setting up the experiment with three replicates, while Casuarina equisetifolia L. was planted as the test crop. Soil sampling for nutrient analysis was conducted quarterly for 12 months to assess nutrient dynamics under different biochar rates in the current study. Compared to soil untreated with Prosopis juliflora biochar, the results showed that there was a significant increase in soil pH by 21% following biochar utilization at the rate of 7.5 t ha-1. Total nitrogen was increased by 32% after the biochar application, whereas the total organic carbon was increased by four folds in comparison to biochar-untreated soil. Available phosphorus was increased by 264% following biochar application in comparison to the control treatment. In addition, the application of biochar resulted in an increment in the soil exchangeable cations (Ca2+, K+, Mg2+) across the assessment periods. Soil cation exchange capacity (CEC), bacteria and fungi were enhanced by 95, 33 and 48%, respectively, following biochar application at 7.5 t ha-1 in comparison to untreated soil. In conclusion, these results strongly suggest improvement of soil biochemical properties following Prosopis juliflora biochar application, thus providing potential for soil fertility improvement in regions such as the one in the study.

A novel iron-based composite modified by refinery sludge for fixing Pb, Zn, Cu, Cd, and As in heavy metal polluted soil: Preparation, remediation process and feasibility analysis

In this study, we prepared a novel iron-based composite (NIC) via a one-step reduction method utilizing refinery sludge (RS) as the reducing agent and iron ore (IO) as the iron source, allowing for the concurrent stabilization of multiple heavy metals (HMs) in soil. The loose, porous structure of NIC provided ample active sites, including Fe0, CaAl2Si2O8, fixed carbon, and a small amount of active amorphous substances. After 60 days of soil remediation using 5% NIC, the bioavailable content of HMs Cu, Zn, Pb, Cd, and As was reduced by 71.55%, 49.62%, 91.35%, 61.37%, and 41.45%, respectively. Upon magnetic recovery and analysis of NIC in soil, HMs were found to have been enriched in the material, forming new phases like FeAsO4, ZnFe2O4, among others. Thus, the immobilization mechanism of HMs included adsorption, co-precipitation and complexation etc. Furthermore, NIC enhanced soil pH and cation exchange capacity, elevating the soil's ability to retain heavy metal cations. Lastly, cost-benefit analysis revealed that RS as a reducing agent could lower the production cost of environmental remediation materials. Furthermore, HM leaching toxicity analysis verified the safety of its usage. Overall, our findings offer a promising procedure for both the resource utilization of refinery sludge and multi-metal co-contaminated soil remediation.

The use of animal manure for improving chemical properties of degraded Ultisol, yield, and secondary metabolic of Zingiber montanum

Ultisols in Indonesia have the potential for agricultural development, but the soils have low pH and nutrient contents that hinder plant growth and yield. Using animal manure can be an alternative to improve soil productivity and crop yields. This study aimed to examine the effects of animal manure on the chemical properties of Ultisol, yield, and secondary metabolic of <em>Zingiber montanum</em>. The treatments tested were combinations of types of manure (cow and chicken manure) and manure application levels, namely P0 (control), P1 (cow manure 20 t/ha), P2 (cow manure 40 t/ha), P3 (cow manure 60 t/ha), P4 (chicken manure 20 t/ha), P5 (chicken manure 40 t/ha), and P6 (chicken manure 60 t/ha). The results showed that the application of chicken manure of 60 t/ha increased N and P contents of the soil, and the application of cow manure of 60 t/ha increased soil cation exchange capacity. The application of cow manure of 60 t/ha gave the highest plant height, the number of leaves, and the number of at 18 weeks after planting, while the application of chicken manure dose of 60 t/ha produced the longest plant roots. The highest fresh and dry rhizome weight was observed for the 60 t/ha cow manure treatment. The highest secondary metabolic levels in each parameter were found in dry rhizomes (phenolic, flavonoid, and tannin) and fresh rhizomes (phenolic and flavonoid), with the highest tannin compound in the treatment of 40 t chicken manure/ha. The application of chicken manure at a dose of 60 t/ha resulted in a strong antioxidant yield in fresh and dry rhizomes.

Preparation of two types plant biochars and application in soil quality improvement

Soil degradation is a global problem that endangers sustainable development. Biochar is a solid, stable, carbon-rich, and highly aromatic material prepared using plant feedstock with a rich pore structure, high specific surface area, and high capacity for holding water and nutrients. This study selected two typical plant resource raw materials, Spartina alterniflora (P. australis) and Spartina alterniflora (S. alterniflora), to prepare biochar at different temperatures, and then investigated the effects of different raw materials and preparation temperatures on the biochar's characteristics. After re-activation treatment, soil improvement experiments were conducted under different carbon application rates. The prepared biochar was alkaline, and contained abundant oxygen-containing functional groups and nutrients (including C, N, Ca, Na, and Mg). Biochar addition had significant effects on the soil microbial community and soil enzyme activity. Finally, by calculating the membership function and factor weights, the various physicochemical and biological properties of the soil were quantified in the form of soil quality indices. The results showed that biochar application had a significant promoting effect on soil quality, mainly through providing rich nutrient sources, enhancing the soil cation exchange capacity and therefore the nutrient effectiveness, and increasing the ability of soil to retain nutrients. The application of biochar (different types) has changed the original nutrient composition, microbial community, and enzyme activity of the soil, and under the combined action of these factors, the soil quality index (SQI) has been improved. This study provides a feasible soil fertility improvement strategy.

Physicochemical properties of environmental media can affect the adsorption of arsenic (As) by microplastics

Microplastics are emerging pollutants that can adsorb heavy metals and threaten human health through food chain. Recently, there has been increasing interest in understanding the adsorption behavior of heavy metals by microplastics in farmland soil. In particular, arsenic (As), as a carcinogen, has the potential to be adsorbed by soil microplastics. However, the mechanisms and controlling factors of As adsorption by microplastics in farmland soil under natural conditions are still unknown. Here, microplastics and As were respectively added to farmland soils with different physicochemical properties from twelve provinces of China for adsorption experiment. We performed surface analysis of microplastics, quantified As accumulation through quasi-first-order kinetic equation and developed regression models to screen the factors controlling As adsorption. The results showed that the adsorption of As by soil microplastics was a chemical process accompanied by the loss of electrons from oxygen-containing functional groups. Soil cation exchange capacity (CEC) was the main factor controlling the adsorption rate, while soil organic matter (SOM), total nitrogen (TN) and CEC mainly influenced the equilibrium adsorption capacity. This is the first report on microplastic-As adsorption in natural soil, which allows deeper insights into risk assessment, prediction and control of microplastic-As pollution in agricultural soil.

Using the quantitative ion character-activity relationships (QICAR) model to predict the solid-liquid release of metals in soil

Dissolved metals in the soil’s liquid phase are more easily absorbed by biological tissues, thus posing potential risks to living organisms. Therefore, studying the solid-liquid partition coefficient (Kd) of metals in the soil helps understand their environmental risks. We collected 102 Kd data of metals in soil from the literature to build a quantitative ion character-activity relationship model (s-QICAR) based on the metals’ physicochemical properties. Correlation analysis showed ten elemental physicochemical properties related to Kd, including covalent bond index, atomic mass, and first hydrolysis constant, with R2 = 0.502–0.989. Through comparative screening, 39s-QICAR models were finally established, including covalent bond index and first hydrolysis constant. The established s-QICAR model predicted the Kd values of Mo, Sb, and La in the 39 soil samples, ranging from 21 to 19978. Finally, a coupling analysis was conducted between Kd-metal and soil physicochemical properties. The s-QICAR model with covalent bond index as the independent variable was mainly affected by soil pH and cation exchange capacity, while the s-QICAR model with first hydrolysis constant was influenced primarily by clay content. Therefore, this study established a predictive model for soil Kd, providing a basis for soil environmental risk assessment and management. Environmental ImplicationDissolved metals present in the soil liquid phase are more easily absorbed by biological tissues, thus posing potential risks to living organisms. Therefore, studying the solid-liquid partition coefficient (Kd) of metals in the soil helps understand their environmental risks. Common Kd values are obtained by measuring the content of soil solid and liquid phase metals. However, this method is time-material consuming. We study the relationship between element properties and their Kd, then establish a model that does not rely on measured data to predict Kd of soil elements, providing a basis for soil environmental risk assessment and management.

Effect of heavy metal co-contaminants on the sorption of thirteen anionic per- and poly-fluoroalkyl substances (PFAS) in soils

Understanding the sorption behavior of per- and poly-fluoroalkyl substances (PFAS) in soils are essential for assessing their mobility and risk in the environment. Heavy metals often coexist with PFAS depending on the source and history of contamination. In this study, we investigated the effect of heavy metal co-contaminants (Pb2+, Cu2+ and Zn2+) on the sorption of 13 anionic PFAS with different perfluorocarbon chain length (C3-C9) in two soils with different properties. Results revealed that Pb2+, Cu2+ and Zn2+ had little effect on the sorption of most short-chain compounds, while the presence of these heavy metals enhanced the sorption of long-chain PFAS in two soils. The distribution coefficients (Kd) of several long-chain PFAS linearly increased with increasing concentrations of heavy metal, especially in the presence of Pb2+ (ΔKd/Δ [Pb2+] > 3 for PFOS and PFNA vs <1 for PFPeS and PFHxS). While several mechanisms may have contributed to the enhancement of sorption of PFAS, the heavy metals most likely contributed through enhanced hydrophobic interactions of PFAS by neutralizing the negative charge of adsorption surfaces in soils and thus making it more favorable for their partitioning onto the solid phase. Moreover, the increase in the concentrations of heavy metals led to a decrease in the pH of the system and promoted sorption of long-chain compounds, especially in soil with lower organic carbon content. Overall, this study provides evidence that the presence of co-existing heavy metal cations in soils can significantly enhance the sorption of long-chain PFAS onto soil, thereby potentially limiting their mobility in the environment.

Temporal Variation in Selection Influences Microgeographic Local Adaptation.

AbstractEcological heterogeneity can lead to local adaptation when populations exhibit fitness trade-offs among habitats. However, the degree to which local adaptation is affected by the spatial and temporal scale of environmental variation is poorly understood. A multiyear reciprocal transplant experiment was performed with populations of the annual plant Leptosiphon parviflorus living on adjacent serpentine and nonserpentine soil. Local adaptation over this small geographic scale was observed, but there were differences in the temporal variability of selection across habitats. On serpentine soil, the local population had a consistently large survival advantage, presumably as a result of the temporal stability in selection imposed by soil cation content. In contrast, a fecundity advantage was observed for the sandstone population on its native soil type but only in the two study years with the highest rainfall. A manipulative greenhouse experiment demonstrated that the fitness advantage of the sandstone population in its native soil type depends critically on water availability. The temporal variability in local adaptation driven by variation in precipitation suggests that continued drought conditions have the potential to erode local adaptation in these populations. These results show how different selective factors can influence spatial and temporal patterns of variation in fitness trade-offs.

Effects of Soil and Water Conservation Practices and Slope Gradient on Selected Soil Physicochemical Properties in Ejersa Watershed, Toke Kutaye District, Ethiopia

This study was conducted to assess the effects of soil and water conservation practices and slope gradients on selected physicochemical properties of soil at Ejersa Watershed based on a total of 18 composite soil samples collected and analyzed using standard laboratory procedures. The values of pH, electrical conductivity, cation exchangeable capacity, organic carbon, organic matter, total nitrogen, and available phosphorus determined in soil samples collected from conserved and nonconserved plots were 6.4 and 6.16, 40.26 mS/m and 15.12 mS/m, 33.51 meq/100 g and 21.56 meq/100 g, 2.66% and 2.24%, 4.58% and 3.86%, 0.24% and 0.15%, and 29.45 ppm and 17.68 ppm, respectively. Soil pH, electrical conductivity, moisture, total nitrogen, and available phosphorus were significantly different ( p &lt; 0.01 ) between treated and untreated plots and among the slope classes. Values of soil organic carbon and organic matter showed significant differences ( p &lt; 0.05 ) between land types but not among the slope classes. Soil cation exchange capacity showed significant difference ( p &lt; 0.05 ) between land types as well as among the slope classes. Relatively, higher values of many of the physicochemical parameters were recorded in samples collected from the treated land and lower slopes which might be attributed to the deposition effects of the conservation practices and decline in the rate of soil erosion.

Geo-environmental and mechanical behaviors of As(V) and Cd(II) co-contaminated soils stabilized by goethite nanoparticles modified biochar

Goethite nanoparticles modified biochar (FBC) could address the weak effectiveness of conventional biochar commonly to process heavy metal(loids) (HMs) co-contamination with different charges. However, few studies have focused on the change of soil mechanical properties after stabilization. In this study, FBC was synthesized to stabilize simultaneously arsenic (As (V)) (anions) and cadmium (Cd (II)) (cations) in co-contaminated soils. Batch adsorption, leaching toxicity, geotechnical properties and micro-spectroscopic tests were comprehensively adopted to investigate the stabilization mechanism. The results showed that FBC could immobilize As (V) mainly through redox and surface precipitation while stabilizing Cd (II) by electrostatic attraction and complexation, causing soil agglomeration and ultimately making rougher surface and stronger sliding friction of contaminated soils. The maximum adsorption capacity of FBC for As (V) and Cd (II) was 31.96 mg g−1 and 129.31 mg g−1, respectively. Besides, the dosages of FBC required in contaminated soils generally were approximately 57% higher than those in contaminated water. FBC promoted the formation of small macroaggregates (0.25–2 mm) and the shear strengths of co-contaminated soils by 21.40% and 8.34%, respectively. Furthermore, the soil reutilization level was significantly improved from 0.14–0.46 to 0.76–0.83 after FBC stabilization according to TOPSIS method (i.e., technique for order preference by similarity to an ideal solution). These findings confirm the potential of FBC in immobilizing As (V) and Cd (II) of co-contaminated soils and provide a useful reference for green stabilization and remediation of HMs co-contaminated sites.Graphical

Key factors influencing arsenic phytotoxicity thresholds in south China acidic soils

Arsenic (As) toxicity threshold values (TTVs) for plants are fundamental to both establishing regional As reference values in soil and performing risk assessment. However, TTVs vary with plant species and soil types. In this study, a hydroponic experiment with 16 plant species was conducted to screen the most As-sensitive plant species. The results showed that the EC20 (available As concentration at which shoot biomass or height is inhibited by 20%) values were 1.38–104.4 mg L−1 for shoot height and 0.24–42.87 mg L−1 for shoot fresh biomass. Rice was more sensitive to As toxicity than the other species. Therefore, it was chosen as the ecological receptor in the pot experiment on As phytotoxicity in nine types of soils collected from Fujian Province in South China. The EC10 and EC20 with respect to rice shoot height were 3.72–29.11 mg kg−1 and 7.12–45.60 mg kg−1, respectively. Stepwise regression analysis indicated that free iron oxide concentration is the major factor that affects As bioavailability in soil, and ECx (x = 10, 20, and 50) of soil available As for shoot height was positively related to free iron oxide concentration in soil. In addition, soil cation exchange capacity, clay (<0.002 mm) content, and exchangeable magnesium content are also important factors influencing As phytotoxicity in acidic soils. The regression models can be used to predict As phytotoxicity in acidic soils.

Biological nitrogen fixation in rice paddy soils is driven by multiple edaphic factors and available phosphorus is the greatest contributor

Biological nitrogen fixation (BNF) is important for sustainable rice cultivation. Various edaphic factors have been individually evaluated for their effects on BNF in paddy soils. However, no single factor could fully explain the different soil outcomes. Paddy BNF is more likely to be simultaneously influenced to various degrees by combinations of several factors; however, the relative importance of the interaction of multiple edaphic factors on the regulation of BNF in rice soils is still unclear. Twenty-seven paddy soil samples with different soil properties were collected from major cropping areas in southwest and northeast China. Rice was transplanted into pots of these soils and grown in a 15N2 enriched airtight chamber. Estimation of BNF was based on measurements of 15N enrichment in the different soils and rice plants at the end of a 77-d incubation period. BNF amounts ranged from 0.66 to 12.3 kg ha−1. BNF had a significant positive relationship with available phosphorus (AP) and significant quadratic relationships with available molybdenum (AMo) and total soil nitrogen (TN). AP explained 42% of the observed variation in BNF, TN explained 17%, and AMo explained 13%. The specific interaction between the soil cation exchange capacity (CEC) and available soil N (ASN, as determined by rice N uptake) accounted for 28% of the variation. BNF was reduced when AP was < 14 mg kg−1, AMo < 0.09 mg kg−1, or when TN was > 3.2 g kg−1. These results provide valuable benchmarks that could be used to guide farmers in managing their soils to improve the potential contribution of paddy BNF to soil fertility.

Microbial siderophores as molecular shuttles for metal cations: sources, sinks and application perspectives.

Iron is one of the highly abundant elements on the earth's crust, an essential micronutrient for a majority of life forms, and exists in two frequent oxidation states such as ferrous (Fe2+) and ferric (Fe3+). These two oxidation states are interconvertible by redox reactions and form complexes with a wide range of siderophores. At neutral pH in soil, Fe2+ is highly soluble upto 100mM but have less biological value, whereas Fe3+ is less soluble upto 10-9M. This reduced bioavailability of Fe3+ induces competition among microorganisms. As many microorganisms need at least 10-6M of Fe3+ form of iron for their growth, siderophores from these microbes readily withdraw Fe3+ iron from a variety of habitats for their survival. In this review, we bring into light the several recent investigations related to diverse chemistry of microbial siderophores, mechanisms of siderophore uptake, biosynthetic gene clusters in microbial genomes, various sources of heavy metal cations in soil, siderophore-binding protein receptors and commercialisation perspectives of siderophores. Besides, this review unearths the recent advancements in the characterisation of novel siderophores and its heavy metal complexes alongside the interaction kinetics with receptors.

Divergent contribution of microbial- and plant-derived carbon to soil organic carbon in Moso bamboo forests left unmanaged

Moso bamboo (Phyllostachys pubescens) has a high carbon (C) sequestration capacity that can help mitigate global climate change. However, owing to strengthened environmental protection policies and rising labor costs, large areas of Moso bamboo forests have been left unmanaged after long-term intensive management. Consequently, the contribution of plant- and microbial-derived C as part of soil organic carbon (SOC) has not been reported in Moso bamboo forests. Here, we investigated the change of microbial necromass and plant-derived components in Moso bamboo forests with different unmanaged chronosequences (i.e., intensively managed currently or unmanaged for 2–5, 7–10, or 11–14 years), using biomarker. We observed that plant-derived C was significantly higher in unmanaged than in intensively managed forests and that the highest content was found in the forests left unmanaged for 7–10 years (3.69 g kg−1). No significant differences in microbial-derived C content were observed between Moso bamboo forests under intensive management and those left unmanaged for 2–5 years. However, compared with intensive management, left unmanaged for 7–10 and 11–14 years significantly increased microbial-derived C content. Overall, the quantitative importance of microbial-derived C as part of SOC was higher than that of plant-derived C (28.7–42.62 % vs 8.88–20.8 %, respectively). Moreover, we found that the major determinants of microbial- and plant-derived C were different. For microbial-derived C accumulation, plant biomass, total nitrogen, total phosphorus, and soluble organic C were the dominant factors, and for plant-derived C accumulation, soil cation exchange capacity was the dominant factor. These findings provide new information about the changes in SOC accumulation in Moso bamboo forests left unmanaged and highlight the different accumulation mechanisms of plant- and microbial-derived C.

Sorption of ionic liquids in soil enriched with polystyrene microplastic reveals independent behavior of cations and anions

Recently, much attention has been focused on the application of the Ionic Liquids (ILs) with herbicidal activity in agriculture. It has been suggested that through the appropriate selection of cations and anions, one can adjust the properties of ILs, particularly the hydrophobicity, solubility, bioavailability, toxicity. In practical agricultural conditions, it will be beneficial to reduce the mobility of herbicidal anions, such as the commonly applied 2,4-dichlorophenoxyacetic acid [2,4-D] in the soil. Furthermore, microplastics are becoming increasingly prevalent in the soil, potentially stimulating herbicidal sorption. Therefore, we investigated whether cations in ILs influence the mobility of anions in OECD soil supplemented with polystyrene microplastic (PS). For this purpose, we used the 2,4-D based ILs consisting of: a hydrophilic choline cation [Chol][2,4-D] and a hydrophobic choline cation with a C12chain [C12Chol][2,4-D]. Characterization of selected micropolystyrene was carried out using the BET sorption-desorption isotherm, particle size distribution and changes in soil sorption parameters such as soil sorption capacity and cation exchange capacity. Based on the batch sorption experiment, the effect of microplastic on the sorption of individual cations and anions in soil contaminated with micropolystyrene was evaluated. The results obtained indicate that the introduction of a 1–10% (w/w) PS resulted in an 18–23% increase of the soil sorption capacity. However, the sorption of both ILs’ cations increased only by 3–5%. No sorption of the [2,4-D] anion was noted. This suggests that cations and anions forming ILs, behave independently of each other in the environment.The results indicate the fact that ILs upon introduction into the environment are not a new type of emerging contaminant, but rather a typical mixture of ions. It is worth noting that when analyzing the behavior of ILs in the environment, it is necessary to follow the fate of both cations and anions.

Leaching of base and metal cations from litter and soils vary in two forest stands with different tree species

Understanding the distribution of cations in forest soils is important for forest management. Here, we evaluated the leaching of cations, potassium (K+), sodium (Na+), calcium (Ca2+), magnesium (Mg2+), iron (Fe3+), aluminium (Al3+), and manganese (Mn2+), from litter through soils in two forest stands with different tree species. We incubated Castanopsis carlesii leaf litter in a Castanopsis carlesii stand and Cunninghamia lanceolata needle litter in a Cunninghamia lanceolata stand using a microcosm method with monthly collections of litter and soil leachates, and the concentrations of cations and fluxes of these cations were assessed separately. We found more Ca2+ but less Na+, Mg2+, and Fe3+ fluxes in litter leaching solutions in Cunninghamia lanceolata than in Castanopsis carlesii stand because of their different initial concentrations in fresh litter. Although cations leached from leaf litter differed among tree species, the leaching fluxes did not vary between stands. Moreover, annual fluxes of cations leached from soils were significantly higher than those from leaf litter, leading to a net loss of soil nutrients to downstream environment. Therefore, the results suggest that reforestation with mixed stands by introducing broadleaved trees in Chinese fir monoculture plantations might reduce soil nutrient loss through the leaching pathway.

Soil dielectric permittivity modelling for 50 MHz instrumentation

Near surface electromagnetic geophysical techniques are proven tools to support soil ecosystem services and soil exploration. Such geophysical techniques provide electromagnetic properties that are useful to characterize the studied soil. The link between relevant soil characteristics and geophysical properties, such as dielectric permittivity (ε), is commonly expressed by pedophysical models. However, some weaknesses remain in their application, such as the requirement of parameters that are difficult to measure or calculate. Therefore, these parameters are frequently fixed, but this oversimplifies the complexity of the investigated soils. Moreover, the validity of ε pedophysical models in the frequency range of operating soil moisture sensors (normally < 100 MHz) remains poorly investigated.In this study, the accuracy and adaptability of ε pedophysical models at different electromagnetic frequency ranges was tested and improved using newly collected laboratory and field data. Such data was collected on soils over a wide range of textures, physical and chemical properties.To achieve this, we review the measurement methods and characteristics of ε pedophysical models, soil phases and geometric parameters. Subsequently, we show how geometric parameters can explain the dependance of soil texture on ε by implementing pedotransfer functions. Then, drawing on a broad experimental basis of common soil types in Europe, we develop novel ε pedophysical models at 50 MHz. These models are not only easy to evaluate but also capture most of the soil’s complexity. Additionally, these new ε pedophysical models eliminate the need for calibration data due to the introduction of novel pedotransfer functions based on soil cation exchange capacity. An extensive model test shows an unprecedented decrease in the RMSE of the newly proposed models of up to 412%.In conclusion, despite it is unlikely to characterize soil structure, bulk density, or temperature at 50 MHz, these updated PPMs are useful for highly accurate water content and ε predictions, in both laboratory and field conditions, without the need for calibration data. As the developed modelling procedures are valid for a wide range of electromagnetic frequencies, these can be applied to soil exploration with TDR and GPR instrumentation.For reproducibility, all collected soil data are provided, alongside open-source Python code that contains the presented modelling procedures.

Leaching amount and timing modified the ionic composition of saline-alkaline soil and increased seed cotton yield under mulched drip irrigation

Salt leaching has been widely applied to increase crop production in saline-alkaline soils. However, leaching patterns affect the ionic composition of saline-alkaline soils and increase seed cotton yield under mulched drip irrigation have been poorly understood. The objective of this study was to determine why leaching patterns succeed to increase seed cotton yield in saline-alkaline soils. A two-year field experiment (2020–2021) was conducted on cotton under mulched drip irrigation to investigate how different leaching amounts and timings modified the ionic composition of saline-alkaline soils and improved the seed cotton yield. There were four leaching amounts (W1: 75, W2: 150, W3: 225 and W4: 300 mm) and three leaching timings (T1: once at seedling stage, T2: twice at seedling and budding stages and T3: thrice at seedling, budding and pollen setting stages) in addition to non-leaching treatment (CK: 85% crop evapotranspiration). Soil cations, soil anions, total dissolved salts (TDS), sodium adsorption ratio (SAR), dry matter accumulation and seed cotton yield were examined. The results showed that increasing the leaching amount significantly reduced soil cations, soil anions, TDS and SAR compared with CK, by 31.85%, 51.82%, 34.83% and 22.20% under W3 over the two years, respectively. The chloride and sulfate in the soil accounted for the majority of TDS (more than 81.03%), suggesting that decreasing chloride and sulfate content in saline-alkaline soils could reduce soil salinity effectively. Increasing leaching amount first increased and then decreased seed cotton yield. Compared with that under CK, the optimal seed cotton yield under W3T2 was increased by 139.42% and 99.06% in 2020 and 2021, respectively. Dry matter accumulation increased with the increase in leaching amount. The Pearson correlation analysis revealed that sodium had the greatest negative effect on seed cotton yield. According to the Technique for Order Preference by Similarity to Ideal Solution, the combination of 225 mm leaching amount and timing of leaching at seedling and budding stages was recommended as the optimal leaching pattern for saving water, controlling salts and increasing yield in this region. Overall, the optimal leaching pattern modified the ionic composition and significantly reduced soil ions in the root zone that were harmful to cotton growth. The study can provide a scientific basis for the rehabilitation of saline-alkaline soils in arid and semi-arid conditions under mulched drip irrigation.

Specific surface area of soils with different clay mineralogy can be estimated from a single hygroscopic water content

The soil specific surface area (SSA) is an important variable for soil science and geoenvironmental engineering applications, but traditional measurement methods are difficult and time-consuming. Regression models or pedotransfer functions are often used to estimate SSA from other soil properties (e.g., clay content and cation exchange capacity), but these models do not consider the impact of clay mineralogy. Hygroscopic water content (wh) is intimately linked to these soil properties, which suggests that wh may be a better parameter for SSA estimation. This study (i) proposes regression models that estimate SSA from wh at different relative humidity values (5 to 90%) for kaolinite-rich samples (KA), illite-rich or mixed clay samples (IL/MC), montmorillonite-rich samples (ML), and a combination of all samples (ALL) and (ii) compares the performance of the wh models to other published models that comprise clay, silt and soil organic carbon contents and cation exchange capacity. We found that the sample-specific wh regression models accurately estimated SSA for KA, IL/MC and ML samples. For KA and IL/MC samples, the performance of the KA model (e.g., for adsorption, average RMSE = 10.5 m2/g) and IL/MC model (average RMSE = 21.3 m2/g) were better than the ALL-calibration model (KA: average RMSE = 18.7 m2/g; ML: average RMSE = 22.4 m2/g). For ML samples, similar model performance between the ML-calibration model (average RMSE = 41.4 m2/g) and the ALL-calibration model (average RMSE = 41.1 m2/g) was observed. In addition, the model performance of regression models based on wh was superior to models published in the literature that are based on clay, silt and soil organic carbon contents and cation exchange capacity. Overall, this study confirms that a single measure of wh can provide reliable estimates of the SSA while revealing a significant impact of clay mineralogy on model performance.

Consequences of elevated CO2 on soil acidification, cation depletion, and inorganic carbon: A column-based experimental investigation

The anthropogenic release of atmospheric CO2 affects soil nutrient cycling through varied biogeochemical processes. Cation depletion from exchange sites, carbonate mineral dissolution, and subsequent changes in organic and inorganic carbon flux are growing concerns for soil health and sustainability. Particularly, the effects of acid deposition on soil pH and soil health under changing global carbon flux is poorly understood. To estimate the magnitude and effects of pH change across different soil profiles, the depth-wise response of soil cations, pH, and soil inorganic carbon (SIC) to varying CO2 levels was investigated using column-leachate experiments. Six soils, representing acidic, neutral, and alkaline pH, were exposed to different CO2 enrichments (100%, 10%, 1%, and Control) of water percolate for 30 days. Analysis of the column leachates revealed that the base cations (Ca, Mg, Na) were higher initially than on day 30, while Si leaching increased with time. The pH in leachates tended to attain an equilibrium state with time under CO2 saturation, indicating the buffering capacity of alkaline and neutral soils. Evaluation of the soil before and after the experiments showed that the solid SIC, such as carbonate minerals and any dissolved SIC components (e.g., carbonate, bicarbonate ions) entrained in the pore space increased, whereas the potential cation exchange capacity (PCEC) decreased in all soils. This trend was especially prominent for alkaline soils at 100% CO2 enrichment. Over the short-term study, the SIC showed minimal response to varying CO2 enrichment conditions in neutral and acidic soils. The altered cation concentrations in the leachates suggest that under long-term exposure to elevated CO2, a deficiency of cationic essential plant nutrients such as Ca2+, Mg2+, and K+ is likely, especially with low buffering capacity and primary mineral content. In contrast, an increase in nutrient solubility and elemental toxicity (e.g., Al3+ Mn) can be observed in the short term. The initial soils with greater ECEC experienced an increased SIC leaching in the shorter term and suggested potential deposition in deeper layers. The resultant SIC loss might be amplified in arid to semi-arid soils with low SIC and affect soil health.